Sur le site Apple, à cette page ci Apple - Upgrade your Mac to OS*X*Mavericks. il précise ceci:

Upgrading from OS X Leopard

If you’re running Leopard and would like to upgrade to OS X Mavericks, first you’ll need to upgrade to OS X Snow Leopard. You can purchase OS X Snow Leopard here.

If you’re running Leopard and would like to upgrade to OS X Mavericks, first you’ll need to upgrade to OS X Snow Leopard. You can purchase OS X Snow Leopard here.
"